As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for secondary batteries has also sharply increased. Among such secondary batteries is a lithium secondary battery exhibiting high energy density and operating voltage and excellent preservation and service-life characteristics, which has been widely used as an energy source for various electronic products as well as various kinds of mobile devices.
Depending upon kinds of devices in which secondary batteries are used, the secondary batteries may be configured to have a detachable type structure in which the secondary batteries can be easily inserted into and removed from external devices or to have an embedded type structure in which the secondary batteries are embedded in the devices. For example, secondary batteries used in the conventional mobile devices are configured to have a detachable type structure in which it is possible for a user to insert or remove a battery into or from each device. On the other hand, secondary batteries used in devices, such as some mobile phones, tablet PCs, and smart pads, may be configured to have an embedded type structure.
Lithium secondary batteries are widely used as such secondary batteries. Each of the secondary batteries includes an anode terminal and a cathode terminal electrically connected to a device, in which the secondary battery is mounted, and a safety element to effectively control an abnormal state, such as overcharge or overcurrent, of the secondary battery. Examples of the safety element may include a positive temperature coefficient (PTC) element, a protection circuit module (PCM), a fuse, and a thermal cutoff (TCO) element.
Generally, a safety element, such as a PCM, is connected to a battery cell, including an anode terminal and a cathode terminal, via a conductive nickel plates by welding or soldering. For example, the nickel plates are connected to the electrode terminals of the battery cell by welding or soldering, a protection circuit board (PCB) is attached to one side of a double-sided tape, a protective tape is attached to the other side of the double-sided tape, and electrode tabs of the PCB and the nickel plates are connected to each other by welding in a state in which the PCB is in tight contact with the battery cell. In this way, the PCM is connected to the battery cell to manufacture a battery pack.
It is required for the PCM to be maintained in electrical connection with the electrode terminals of the battery cell and, at the same time, to be electrically isolated from other parts of the battery cell. To this end, insulative tapes are attached to various members, including the PCM. In addition, a sealed portion of a battery case is partially bent, and an insulative tape is attached thereon or a barcode is printed thereon. That is, the process is very complicated.
Since a plurality of insulative tapes or parts is required to achieve safe connection between the safety element and the battery cell as described above, a battery pack assembly process is complicated, and manufacturing cost is increased. Also, when external impact is applied to a battery pack, the PCM may be damaged or dimensional stability may be greatly lowered due to the use of the insulative tapes, which exhibit low mechanical strength.